In general, a MOSFET has a structure including a gate electrode, a source/drain electrode, and an oxide layer therebetween, which are formed on a silicon substrate.
Recently, as semiconductor devices have become highly integrated, miniaturized, and lightweight, physical size of the MOSFET is scaled down, thereby decreasing a valid channel length and causing a short channel effect deteriorating a punch-through between a source and a drain.
To resolve such problems, a source/drain formed in a lightly doped drain (hereinafter referred to as “LDD”) structure have been proposed. The source/drain has a shallow junction to decrease the short channel effect. However, in a highly integrated semiconductor device having a MOSFET with a smaller line width, it is difficult to fabricate the LDD structure.
Meanwhile, U.S. Pat. No. 6,521,508 discloses a method for manufacturing a contact plug in a semiconductor device using a selective epitaxial silicon growth process, and U.S. Pat. No. 5,633,201 discloses a method for forming tungsten (or aluminum) plugs in contact holes of highly integrated semiconductor device. However, as a semiconductor device becomes highly integrated and,miniaturized, contacts connected with the gate electrode, a bit line and contact holes therefore are getting smaller. Accordingly, a contact hole manufacturing process for forming the contacts or contact plugs by depositing a conductive material into the contact holes comes to have limitations when the contact holes are formed in the highly integrated semiconductor device.